This invention relates to a combustion detecting element for detecting incomplete combustion of a burner.
Various devices are known in the prior art for detecting incomplete combustion having an element body made of zirconia or the like which generates an electric change, for instance, electromotive force, corresponding to an oxygen concentration difference between one side surface of the body and the other side surface of the body. These devices are generally provided on both side surfaces with equal-sized catalytic electrode layers, for instance, porous platinum electrode layers for carrying out a catalytic reaction with combustible gas.
The element is, for instance, with one side surface (hereinafter the "first surface") thereof facing a burner to be monitored while the other side surface (hereinafter "the second surface") thereof is exposed to a combustion flame of a standing burner, which is burning continuously and impinging on the second surface. With this arrangement, oxygen is consumed in a catalytic combustion reaction of the combustible gas in the flame of the standing burner in the catalytic electrode layer on the second surface. As a result, the oxygen concentration on the second surface side is lowered. In a normal condition, a difference in oxygen concentration is obtained between the second surface and the first surface. However, if there occurs incomplete combustion of the burner being monitored, the flame of the burner contacts the catalytic electrode layer on the first surface. The oxygen concentration on the first surface is lowered by consumption of oxygen caused by the catalytic reaction which is the same as that occurring in the second surface. Thus, the oxygen concentration difference between the two surfaces is decreased and an electric change corresponding to this is produced in the element. In this manner, incomplete combustion in the burner being monitored can be detected. However, a certain disadvantage is present in these prior art devices in that the catalytic reaction of the combustible gas contained in the flame of the standing burner on the catalytic electrode layer on the second surface reduces the oxygen concentration on the second surface to a tremendous degree. It takes a large amount of time before the oxygen concentration on the first surface is lowered enough to a predetermined value in comparison with the oxygen concentration on the second surface after the flame of the burner being monitored comes into contact with the catalytic electrode layer on the one side surface because of incomplete combustion. Thus, these devices are not quickly responsive.